Field of the Invention
The present invention relates to an image pickup apparatus, such as a digital single lens reflex camera, having a semi-transparent mirror that divides object light into an image pickup device and a finder optical system.
Description of the Related Art
There is an image pickup apparatus, such as a digital single lens reflex camera, that allows a part of object light passing through a lens unit transmit a semi-transparent mirror to expose an image pickup unit and reflects the remaining part of the object light to a finder optical system for observation by the semi-transparent mirror.
As such an image pickup apparatus, there is a conventionally proposed technique that rotates a shading member, which is rotatably supported by a holding frame for a quick return mirror including a transflective portion, to a position close to the holding frame by urging force of a toggle spring in a mirror-up state and rotates the shading member to a position apart from the holding frame in a mirror-down state. In this proposal, the toggle spring is hung between a mirror box and the shading member at an object side of the holding frame (Japanese Laid-Open Patent Publication (Kokai) No. H11-295810 (JP H11-295810A)).
However, the technique disclosed in the above-mentioned publication restricts a size of a toggle mechanism including the quick return mirror in order to avoids interference between the toggle spring and a lens at an image-plane side of a lens unit because the toggle spring is projected to the object side at the time when the quick return mirror is in the mirror-down position. Accordingly, since the quick return mirror cannot be enlarged, an exposure area of the object light on the image pickup device is narrow. Moreover, since the toggle spring is exposed to a photographing light path in the mirror-down state as mentioned above, unnecessary reflected light may occur at a time of photographing.
Moreover, a digital single lens reflex camera has a semi-transparent mirror that is arranged in a photographing light path. A part of object light passes through the semi-transparent mirror to an image pickup device that functions as an AE-AF sensor. The remaining part of the light is reflected by the semi-transparent mirror toward an optical finder so as to enable to observe an object. This configuration may cause a problem in that incident light from the finder entering into a mirror box through the semi-transparent mirror enters into the image pickup device and causes flare in the mirror-up state. Although a conventional camera having a sub mirror solves the problem of flare by covering a semi-transparent mirror with the sub mirror in a mirror-up state, a camera without a sub mirror needs to take a new measure.
In order to prevent the flare in the mirror-up state, the above-mentioned publication proposes a configuration that drives a shading member that rotates around a distal end of the holding frame for the quick return mirror to a position close to the quick return mirror in the mirror-up state and drives the shading member to a position apart from the quick return mirror to be retracted from an AF-AE optical path in the mirror-down state.
Incidentally, it is necessary to reserve the transflective portion of the quick return mirror widely in order to enlarge an AE-AF area in the image pickup device in the mirror-down state. On the other hand, the shading member needs to be shaped so as to shade the transflective portion certainly in order to prevent the light from the finder from entering into the image pickup device in the mirror-up state at the image pick-up time. Although the wide transflective portion needs to increase the area of the shading member, such enlargement is difficult because of a space restriction inside the mirror box.
However, although the above-mentioned publication discloses that the holding frame is driven interlocked with the shading member, a concrete relation between the holding frame and the shading member is not described, and details about shading are not analyzed.